The subject invention is directed toward the art of pressure relief valves and, more particularly, to a flap type valve structure capable of variable valving to satisfy different pressure relief demands.
The invention is especially suited for use in motor vehicle ventilation systems and will be described with particular reference thereto; however, the invention is capable of broader application and could be used to provide variable pressure relief valving in many different systems.
The passenger compartments of motor vehicles must generally be provided with pressure relief valves to relieve the pressure within the compartment and to permit the exhausting of air to the exterior while preventing the undesired reverse flow of air to the interior. The typical relief valve is a flap valve mechanism wherein a flap of flexible material is suspended in a frame and rests by gravity in a closed position against a valve seat frame.
The positioning of the flap relative to the seat is such that it acts like a check valve and can open only when compartment pressure is in excess of exterior pressure by a certain minimum. When there is a relatively low constant pressure relief requirement such as is produced by a ventilating system blower, the typical prior art valves function adequately. However, when there is a high internal pressure pulse, such as results when a door is slammed shut, it would be desirable to have the valves provide a significantly higher and variable discharge rate.